The isoenzymes of glucose-6-phosphate dehydrogenase (G-6-PD) will be used as cellular markers in black females heterozygous for G-6-PD to test whether the gelatinous lesion is the precursor of the fibrous plaque. Histochemical methods will be used to attempt to identify clones of cells on a microscopic basis and studies on thrombi will be continued. BIBLIOGRAPHIC REFERENCES: The human atherosclerotic plaque: Pearson TA, Kramer EC, Solez K, Heptinstall RH. Amer J Pathol 86: 657-664, 1977. Patterns of clonal growth within large atherosclerotic fibrous-capped plaques: Pearson TA, Dillman J, Kramer EC, Solez K, Heptinstall RH. Amer J Pathol 86:53a, 1977 (abstract).